The invention relates to an injection moulding apparatus with mould mounting plates carrying mould tools and a lubricant pump supplying a plurality of locations and at least one machine part movable by a hydraulic drive.
The invention relates to an injection moulding apparatus with mould mounting plates carrying mould tools and a lubricant pump supplying a plurality of locations and at least one machine part movable by a hydraulic drive.
In conventional injection moulding machines a central hydraulic pump is driven by an electric motor. The pressure fluid actuates piston-cylinder units for closing the mould, for maintaining a closure pressure, for opening the mould and for injecting the plasticised plastic material. It is only the plasticisation of the plastic material that is effected by a rotary movement, namely the rotary movement of the plasticising screw which is produced by a hydraulic motor driven by the hydraulic fluid.
Hydraulic drives seem to be the ideal drive technology for injection moulding machines if it is considered that in this case it is almost exclusively linear movements of a defined length that are executed, at the end of which typically a constant pressure (closing pressure, contact pressing pressure, holding pressure) is to be maintained. Nonetheless, fully electric injection moulding machines have become widespread over the last two decades, in regard to which it is not sufficient for the injection procedure to be implemented by a servomotor which can be well controlled. With regard to the avoidance of energy losses but in particular also contamination and disposal problems when connecting all moving parts of the machine to the central hydraulic pump, the described linear drives are implemented by three-phase motors, the rotary movement of which is converted into a linear movement again by spindles or the like.
If in accordance with those lines of argument the provision of a hydraulic motor in the injection moulding apparatus is relinquished, it is necessary at the present time to come to terms with the fact that an electric motor in itself is rather unsuitable for many tasks. That applies in particular where the drive produces a slight movement only after long intervals of time and moreover is to hold a high pressure.
The invention now starts out in terms of the consideration that even a so-called fully electrical machine cannot forego the lubrication of various bearing locations and for that purpose has a central lubricant pump from which lines lead to the individual bearing locations. This means that a system is available in such machines, which system provides a fluid under high pressure at any time. The invention provides that this system for energy supply is associated with a hydraulic drive of the injection moulding machine, in particular the fixing device for the mould tools.
In carrying out the concept of the invention it is in itself possible to operate the hydraulic drive, for example that of the clamping device for the mould tools, directly with the lubricant. As the experience in that respect is still slight, it is also possible to associate with the hydraulic drive its own fluid circuit which is put under pressure by way of the lubricant pump. In that way, the principle of the installation which is completely free from hydraulic fluid is admittedly mitigated somewhat, but the essential advantage of the fully electrical machine, namely foregoing its own hydraulic pump together with the associated lines and conduits, is maintained.
Details of the invention are described hereinafter by means of embodiments.